1. Field of the Invention
The invention relates to a novel printing process and to the press for implementing this process.
2. Description of the Related Art
The process of the invention is a hybrid process, combining in some way the techniques and advantages of current magnetography with the techniques of magnetolithography as they have been described in French Patent Application 93 00301, filed on Jan. 14, 1993 and assigned to Nipson, entitled "Procede d'impression et presse pour la mise en oeuvre" [Printing Process and Press for Implementing It], and the techniques of electrostatography.
U.S. Pat. No. 5,129,321 assigned to Rockwell International Corporation discloses a lithographic printing system that makes it possible to dispense with the use of an engraved plate and hence with the positioning and adjustment thereof, but it has the disadvantage of not being perfectly suitable to high press runs.
In this lithographic printing system, in order to print with the aid of a conventional (oleaginous) ink, the invention in fact consists of replacing the assembly constituted by the engraved plate and the plate cylinder with a simple cylinder on whose periphery a layer forming a substrate of a powdered oleophobic material is deposited, each time a new motif is to be printed; with the aid of a hardenable oleophilic material, an image corresponding to the motifs to be printed is deposited on this uniform layer. The intermediate transfer element is accordingly constituted by the substrate of oleophobic material and the zones of oleophilic material carried by this layer.
Preferably, the oleophobic material is magnetic, and the cylinder is magnetizable, so that the layer of this material will be held on the periphery of the cylinder, magnetizing it.
Depositing the oleophilic material in a configuration corresponding to the motifs to be printed is done with the aid of an electronic, electromechanical or electromagnetic transfer device, for transferring data representative of the motifs to be placed on the layer of oleophobic material, the data being contained in an electronic memory. This data is utilized so that the transfer device deposits the oleophilic material solely at the locations necessary on the oleophobic layer. In an implementation described in the aforenoted patent, the oleophilic material used is a magnetic fusible material; its deposit on the substrate of oleophobic material is done by magnetodeposition on the cylinder, in the way in which magnetic toner is deposited in magnetographic printers. To that end, magnetic heads are disposed in proximity with the cylinder, and they make it possible to create on the substrate zones whose magnetization makes it possible to attract the particles of oleophilic material.
After its deposition, the oleophilic material is fused, which enables it to harden, so as on the one hand to prevent the motifs from deforming and on the other to lend it a certain cohesion with the substrate of oleophobic material, with the particles of oleophilic material attaching to the particles of oleophobic material. To that end, the system described in the aforementioned patent further includes, in proximity with the periphery of the cylinder, a fuser device for fixing the oleophilic material.
Printing is done as on a conventional press: the cylinder, after having been coated with the layer forming the substrate and the motifs, is set into rotation, then moistened and inked, in such a way that the ink spreads over the motifs and the moistening product spreads over the oleophobic zones, and then the ink is transferred to the printing carrier (paper or other material) by way of a blanket.
Once the desired run of an image is reached, the cylinder is demagnetized, so that the layer forming the substrate spontaneously detaches from the cylinder, bringing with it the hardened motifs of oleophilic material that it carries. If printing of another image is desired, then a new substrate is made, on which new motifs are deposited and then hardened. Both the making up of the motifs corresponding to an image and their removal are accordingly very fast and less expensive than with conventional presses.
This apparatus is capable of polychrome printing, to the extent that the positioning of the motifs is done automatically, by an electronic device.
However, it requires the deposit of two types of materials: that making up the substrate, and that making up the motifs. Depositing the substrate has the function of enabling easy later removal of the oleophilic motifs by forced detachment from the substrate, and of preventing the ink from being deposited on the portions of the cylinder that are not provided with oleophilic material.
In addition, it is not actually suitable for high press runs, because the substrate has a tendency to spontaneous detachment, at least in some regions, when the carrier cylinder rotates during the printing phases, since it is held merely magnetically. Accordingly, the outgoing copies have to be checked, and sometimes the image (substrate and motifs) on the periphery of the cylinder have to be reconstituted during the run.
U.S. Pat. No. 3,804,511 assigned to Pelorex Corporation also discloses a printing apparatus and process for an image for transfer of at least one colorant vehicle between an intermediate transfer element and a printing carrier, including at least one phase of automatically making the intermediate transfer element by developing zones on the intermediate element, each zone having a different affinity for the colorant vehicle. The different affinity of the zones is obtained by developing an electrostatic image of the graphical information by exposing an endless strip whose upper layer is made up of zinc oxide. Particles of magnetic toner are then applied to that surface and adhere as a function of the electrostatic image developed on the layer of zinc oxide. Portions of this surface are magnetized to form a magnetic image corresponding to the electrostatic image. Next, the toner particles are transferred by pressure to a copying medium, such as paper, while the magnetic image is preserved on the surface of the strip. New magnetic particles can then be applied to the magnetic image to produce additional copies.
Such an apparatus has the disadvantage of using a strip or tape of zinc oxide, which is a first generation photoconductor whose service life is very short.
On the other hand, if such a tape is not to succumb to fatigue, the cycling time between the exposure of an image and the resetting to zero of the strip to change the image must be quite long, that is, on the order of one second. This accordingly requires tapes of very great length and involves high expense for the equipment.